1. Field of the Invention
The present invention generally relates to a semiconductor device and, more particularly, to a surface-mountable semiconductor device having a plurality of semiconductor elements integrated in a one-piece package and a method of manufacturing such a semiconductor device.
2. Description of the Related Art
Recently, high-density integration of semiconductor chips has advanced, and the size of the semiconductor chip has been reduced. Therefore, the pitch of the projection electrodes to mount the semiconductor chip on a circuit board or substrate is also reduced. Arrangement of the projection electrodes for surface mounting has changed from a peripheral arrangement to a so-called area bump arrangement in which the projection electrodes are arranged over the entire mounting surface of the semiconductor chip. Such a surface-mountable semiconductor device is manufactured by forming a redistribution layer (generally referred to as an interposer) on a single semiconductor chip and forming the projection electrodes on the redistribution layer. That is, the mounting surface of the semiconductor device is effectively used by arranging the projection electrodes at appropriate positions on the redistribution layer.
On the other hand, a technique has been developed to cut out each semiconductor chip from a wafer on which a plurality of semiconductor chips are formed after electrodes of each of the semiconductor chip are rearranged. Such a technique is referred to as a wafer level packaging technique.
However, there is a limit in reducing the pitch between the projection electrodes due to the restrictions from the structure of the projection electrodes and the structure of the board to which the semiconductor device is mounted. Accordingly, when the area of the mounting surface is reduced due to the reduction in the size of the semiconductor chip, it becomes difficult to form a necessary number of projection electrodes within the limited mounting area.
That is, if the projection electrodes are provided in the entire mounting area of the semiconductor chip in accordance with the area bump structure, it is difficult to further reduce the size of the semiconductor chip. In such a case, a so-called fan-out structure must be adopted in which the projection electrodes are arranged outside the semiconductor chip. However, the use of the fan-out structure cannot reduce the size of the semiconductor device even though the size of the semiconductor chip is reduced.
Additionally, in a case in which the semiconductor device is fabricated by narrowing the pitch of the projection electrodes to the limit, a high density surface mounting technique must be used to mount such a semiconductor device. Thus, there is a problem in that a user who does not have such a high density surface mounting ability cannot use such a semiconductor device.
It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor device having a plurality of semiconductor chips incorporated in a one piece package so as to substantially increase the mounting area of the semiconductor device so that the semiconductor device is provided with the projection electrodes having a structure which enable the semiconductor device to be mounted by a conventional surface mounting technique.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising:
a plurality of different kinds of semiconductor elements providing a complete function as a whole;
a redistribution layer interconnecting and integrally holding the plurality of different kinds of semiconductor elements so that the plurality of different kinds of semiconductor elements together provide the complete function; and
a plurality of projection electrodes provided on the redistribution layer for surface mounting.
According to the above-mentioned invention, because the plurality of semiconductor elements are electrically connected to each other by the redistribution layer and integrated in the same semiconductor device, the plurality of semiconductor elements together can be mounted on a circuit board by mounting the semiconductor device on the circuit board and there is no need to individually mount each of the plurality of semiconductor elements to the circuit board. Thereby, the number of processes required for mounting the semiconductor elements is reduced.
Additionally, because the plurality of semiconductor elements arc electrically interconnected by the redistribution layer, a number of projection electrodes necessary for the semiconductor device is smaller than the sum of the number of electrodes on the plurality of semiconductor elements. Accordingly, if the projection electrodes provided to the semiconductor device are formed in accordance with a structure of projection electrodes which enables use of a conventional surface mounting technique, the projection electrodes can be arranged within the mounting surface of the semiconductor device. Additionally, if there is an unoccupied area in one of the mounting surface of the plurality of semiconductor elements, the unoccupied area can be used for mounting other semiconductor chips for which an insufficient mounting area exists, since the mounting surfaces of the plurality of semiconductor chips can be commonly used. Thus, the number of necessary projection electrodes can be formed within the mounting area of the semiconductor device.
Additionally, because the plurality of semiconductor elements are integrated in the one piece package and electrically connected to each other, the mounting area can be reduced to a size less than that in which the plurality of semiconductor elements are individually mounted on the circuit board. That is, there is no need to provide wiring that connects the plurality of semiconductor elements on the circuit board side to which the semiconductor device is mounted, and, thus, the area previously used by the wiring can be eliminated.
Additionally, because the plurality of semiconductor elements are arranged close to each other and are connected by the redistribution layer, the distance between the semiconductor chips are extremely short. Thus, the lengths of signal transmission lines between the semiconductor elements are short, which enables high-speed operation.
In the above-mentioned structure, a complete function can be provided by the plurality of semiconductor elements as a whole by rendering the plurality of semiconductor elements to be different kinds.
Additionally, in the semiconductor device according to the present invention, at least one of the plurality of different kinds of semiconductor elements may be stacked on another one of the plurality of different kinds of semiconductor elements.
Accordingly, a plurality of semiconductor elements can be efficiently accommodated in the package without increasing the mounting area of the semiconductor device.
Additionally, there is provided according to another aspect of the present invention a semiconductor device comprising:
a plurality of the same kind of semiconductor elements;
a redistribution layer interconnecting and integrally holding the plurality of the same kind of semiconductor elements; and
a plurality of projection electrodes provided on the redistribution layer for surface mounting.
According to this invention, when a lot of the same kind of semiconductor elements are to be mounted on a circuit board, the plurality of semiconductor elements provided in the semiconductor device are rendered to be the same kind so that a mounting area corresponding to the plurality of semiconductor elements is reduced.
Additionally, the plurality of the same kind of semiconductor elements may be formed on the same wafer and cut out from the wafer in one piece. Accordingly, a process of cutting out an individual semiconductor element can be eliminated. Additionally, since an accurate positional relationship in a wafer state can be maintained, a process of positioning the plurality of semiconductor elements can be simplified.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor device, comprising the steps of:
arranging a plurality of semiconductor elements adjacent to each other;
forming a redistribution layer over the plurality of semiconductor elements so as to interconnect and integrally hold the plurality of semiconductor elements; and
forming a plurality of projection electrodes on the redistribution layer for surface mounting.
According to the above-mentioned invention, since the plurality of semiconductor elements are electrically connected to each other by the redistribution layer and integrated in the same semiconductor device, the plurality of semiconductor elements together can be mounted on a circuit board by mounting the semiconductor device on the circuit board and there is no need to individually mounting each of the plurality of semiconductor elements to the circuit board. Thereby, the number of processes for mounting the semiconductor elements is reduced.
Additionally, since the plurality of semiconductor elements are electrically interconnected by the redistribution layer, a number of projection electrodes necessary for the semiconductor device is smaller than the sum of the number of electrodes on the plurality of semiconductor elements. Accordingly, if the projection electrodes provided to the semiconductor device are formed in accordance with a structure of projection electrodes which enables use of a conventional surface mounting technique, the projection electrodes can be arranged within the mounting surface of the semiconductor device. Additionally, if there is an unoccupied area in one of the mounting surface of the plurality of semiconductor elements, the unoccupied area can be used for other semiconductor chips having an insufficient mounting area since the mounting surfaces of the plurality of semiconductor chips can be commonly used. Thus, the number of necessary projection electrodes can be formed within the mounting area of the semiconductor device.
Additionally, since the plurality of semiconductor elements are integrated in the one piece package and electrically connected to each other, the mounting area can be reduced less than that when the plurality of semiconductor elements are individually mounted on the circuit board. That is, there is no need to provide wiring that connects the plurality of semiconductor elements on the circuit board side to which the semiconductor device is mounted, and, thus, the area occupied by the wiring can be eliminated or used for other purposes.
Additionally, since the plurality of semiconductor elements are arranged close to each other and are connected by the redistribution layer, the distances between the semiconductor chips are extremely short. Thus, the lengths of signal transmission lines between the semiconductor elements are short, which enables a high-speed operation.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor device, comprising the steps of:
forming a plurality of semiconductor elements on a wafer;
forming a redistribution layer on the wafer so as to electrically interconnect a predetermined number of the semiconductor elements formed on the wafer;
cutting out the predetermined number of the semiconductor elements from the wafer in one piece; and
forming a plurality of projection electrodes on the redistribution layer for surface mounting.
According to this invention, since the predetermined number of semiconductor elements are cut out from the wafer in one piece, a process of cutting out individual semiconductor elements can be eliminated. Additionally, since an accurate positional relationship in a wafer state can be maintained, a process of positioning the plurality of semiconductor elements can be simplified.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor device, comprising the steps of:
placing a first semiconductor element on an electrode surface of a second semiconductor element and fixing the first semiconductor element to the second semiconductor element, the first semiconductor device being smaller than the second semiconductor element;
forming a redistribution layer over the first and second semiconductor elements so as to electrically interconnect the first and second semiconductor elements; and
forming a plurality of projection electrodes on the redistribution layer for surface mounting.
According to this invention, since the first semiconductor element is stacked on the second semiconductor element, the first and second semiconductor elements can be efficiently accommodated in the package without increasing the mounting area of the semiconductor device.